Continuous polymerization processes and resulting products



Patented Apr. 13, 1954 CONTINUOUS POLYMERIZATION PROC- ESSES AND RESULTING PRODUCTS Gerald R Barrett, Winchester, Mass, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application June 28, 1950, Serial No. 170,955

I 13 Claims.

The present invention relates to a. continuous process of polymerizing a monomer or monomers of polymerizable unsaturated organic compounds, and it more particularly relates to a continuous process of polymerizing one or more polymerizable unsaturated organic compounds in an inert liquid which is a solvent for such compounds but not a solvent for polymeric materials derived from such compounds. The present invention also relates to polymeric materials having novel physical properties.

It has been proposed heretofore to polymerize styrene together with maleic anhydride in an aromatic hydrocarbon liquid such as xylene by heating the batch until the conversion of styrene and maleic anhydride monomers is substantially complete. During the polymerization the styrene-maleic anhydride copolymer separates from the liquid in the form of extremely fine particles and when the reaction has been carried out to the desired extent, the copolymer is separated from liquid and is then subjected to a stream of hot air to evaporate the liquid contained in the copolymer. This process has a number of disadvantages. In the first place, considerable equipment and labor is required to operate the process on a commercial scale. Secondly, on removal of the copolymer from the liquid by filtration, or centrifuging, large amounts of the liquid, for example, from 70 to 80% by weight areretained by the copolymer with the result that recovery of the liquid for further use is made difiicult and expensive. Thirdly, the copolymer is obtained in the'form of extremely fine particles which have an apparent bulk density of 13 to 17 pounds/cubic foot. This product is extremely difiicult to handle because ofdusting and the electrostatic charge efiects exhibited by the ma terial. Moreover, shipping and packaging costs of the product are high because of its low apparent density. Fourthly, the process must generally be carried out at monomer concentrations of 10 to 15% based on the-weight of the batch with the result that large amounts of the aromatic hydrocarbon liquid must be used andthis further increases the cost of the process.

The above batch process for preparing styrenemaleic anhydride copolymers is frequently referred to as a solvent-non-solvent process for the reason that the aromatic hydrocarbon liquid used is a solvent for the styrene and maleic anhydride monomers but is a non-solvent for the copolymer formed by the copolymerization of such monomers. Other polymeric materials have been prepared batohewise by a similar process and the difficulties experienced in the styrenemaleic anhydride batch process have also been experienced in the preparation of such polymeric materials.

In accordance with the present invention, it is possible to continuously polymerize styrene and maleic anhydride and other polymcrizable unsaturated compounds or mixtures of polymerizable unsaturated compounds without the disadvantages which have heretofore been encountered in batch solvent, non-solvent polymerize. tion processes. Thus, it is possible, in accord ance with the present invention, to provide polymeric materials on a commercial scale with a.

minimum amount of equipment and] labor. It is also possible to cut down considerably on the amount of hydrocarbon or other inert liquid required, and to reduce the cost involved in recovering such liquid. Moreover, it is also possible to produce a product of larger particle size, which product is substantially free of dusting and has an apparent density considerably higher than that obtainable by batch processes.

It is one object of the present invention to provide a continuous process for polymerizing monomer of polymerizable unsaturated organic compounds and to reduce the costs of operation as compared with a batch process.

A further object of this invention is to provide a continuous process for polymerizing monomers of polymerizable unsaturated organic compounds in a non-polymerizable, inert liquid which is a solvent for the unsaturated organic compounds but is a non-solvent and non-swelling medium for the polymeric materials derived fromv such compounds.

A further object of the invention is to provide a continuous process for preparing polymeric materials of large particle size and high apparent density.

Still further objects and advantages of the present invention will appear from the following description and the appended claims. Before explaining in detail the present invention, however, it is to be understood that the invention is not limited in its application to the details described herein, since the invention is capable of other embodiments and of being practiced or carried out in various ways.

The processes of the present invention are carried out, in general, by continuously adding a polymerization catalyst, one or more monomeric polymerizable unsaturated organic compounds and a non-polymerizable, inert liquid which is a .solvent for such compound or compounds but is a non-solvent and non-swelling medium for polymeric materials resulting from the polymerization of such unsaturated compound or compounds, to a slurry, paste or suspension of a polymeric material obtained by the polymerization of such unsaturated compound or compounds, in a non-polymerizable, inert liquid which is a solvent for such unsaturated compound or compounds but is a non-solvent and non-swelling medium for the polymeric materials, which liquid also contains a polymerization catalyst and a minor proportion, for example, between 1 and 8% by weight of unreacted monomers. The temperature of the slurry or suspension is continuously maintained sufliciently high to effect reaction or polymerization between the monomers in the liquid thereby forming additional polymeric material which is insoluble in the liquid. A portion of the slurry is removed continuouslyfrom the reaction zone, or the main portion or body of the slurry. The amount of slurry removed over any one increment of time may be less than, equal to, or greater than the amount of monomer, catalyst, and liquid added to the main portion ofthe slurry over the same increment of time. a

For ease of operation and most satisfactory results, it is preferred to withdraw orremove from the main portion of slurry, an amount of slurry which is substantially equal to the amount of monomers, catalyst and inert liquid added to the slurry, that is, theadditions to and with drawals from the main portion of slurry or suspension are preferably made at such a rate that the volume of the main portion or" the slurry is maintained substantially constant. The minor portion or increment of slurry may be removed continuously from the main portion of slurry by a constant overflow arrangement or by gravity flow or a pumping arrangement which removes the slurry from any level of the main portion of the slurry. The polymeric material, in the slurry thus removed, is separated from the major portion of inert liquid, catalyst and unreacted,

monomer or monomers as by filtration, centrifuging or the like, and then subjected to a current of hot air, or steam, if the polymeric material is not water-soluble, to remove a substantial portion of the remaining liquid, monomers etc. The recovered liquid, monomers and catalyst may be, and preferably are, used for further additions to the main portion of the slurry.

By carrying out the above describedrprocess, it is possible to obtain polymeric materials of iarge particle size and which are substantially free of dusting. It 'is also possible to obtain polymeric materials having an exceedingly high apparent density as compared to the corresponding polymeric materials which are produced by batch processes.

The initial slurry or suspension of polymeric materials to which the monomer or monomers, inert liquid and catalyst are continuously added and from which the minor portion of slurry or suspension is continuously withdrawn may be prepared in various ways. Thus, it is possible to prepare the slurry or suspension in accordance with the well-known batch processes. For example, it is possible to polymerize the monomers in the inert liquid by heating in the presence of a catalyst without adding additional mono- For convenience of description the processes of the present invention will be described in greater detail with reference to the continuous polymerization of styrene and maleic anhydride monomers, but it is to be understood that the processes described herein are applicable to the polymerization of a large variety of monomers and mixtures of monomers as will be pointed out in greater detail in the following description and the exmers and without withdrawing or removing poly- I meric materials, until from about 80 to 95% conversion of monomer or monomers to polymeric material is efiected.

amples. A slurry or suspension of styrene-maleic copolymer in a non-polymerizable, inert hydrocarbon or chlorinated hydrocarbon liquid is first prepared according to the well-known batch processes or, for example, by heating styrene and maleic anhydride monomers dissolved in a suitable hydrocarbon liquid such as benzene containing from about 0.02 to 0.3% of a polymerization catalyst such as benzoyl peroxide until from about to conversion of the monomers to a styrene-maleic anhydride copolymer is obtained. It is convenient to start with a solution containing from about .10 to 20% by weight of the monomers. In most instances it is desirable to obtain a slurry which contains substantially the same molecular proportions of unreacted styrene and maleic anhydride monomers and,.

since the copolymer generally contains the styrene and maleic anhydride combined in substantially equimolecular proportions, it is preferred to start with a solution containing substantially equimolecular proportions of styrene and maleic anhydridemonomers.

After the initial slurrycr suspension of styrene-maleic anhydride copolymer inthe hydroto add a solution containing the hydrocarbon or chlorinated hydrocarbon liquid, the monomers and the catalyst, although each of the ingredients may be added separatelyif desired. The rate of addition may be varied to a considerable extent depending upon the rate of reaction which is in turn governed by the temperature of the slurry, the polymerization catalyst and the amount thereof used and the mol or weight ratio of styrene to maleic anhydride, and the amount of conversion of monomers to polymer desired. In those instances where it is desired to keep the amount of unreacted monomers in the slurry at a minimum, and to operate at high reaction rates, it is preferred to add the monomers, hydrocarbon or chlorinated hydrocarbon liquid and catalyst at such a rate as to replace from about 8 to 12% by weight of the initial 7' slurry per hour, that is, the additions are preferably made at the rate of 8 to 12% by weight,

based on the initial slurry weight, per hour.

The weight ratio of monomers, hydrocarbon or chlorinated hydrocarbon liquid and catalyst I i added to the copolymer slurry maybe varied con siderably. For best results, it is preferable to add these ingredients in such proportions that from 20 to 40 parts by weight of monomers are added for every 80 to 60 parts of hydrocarbon or chlorinated hydrocarbon liquid and 0.02 to 0.3

by weight of monomers, from 80 to 60 by weight memam of "the hydrocarbon or chlorinated ;:hydmcarbon liquid-.airxdifi'omzoioz'to 0.3% by weight of Q3013?- merization catalyst.

The weight or zmoliratio ofsstyrene to maleic anhydride may be varied considerablmior example, the weight ratio of styrene to "maleic anhydride may be varied between .9 parts by weight. ofstyrene ta 1 part'byaweight of maleic anhydride and i part by weight of styrene to 1.5 parts by weight of maleic anhydride. There is ordinarily, however, nouadvantage in using excess styrene or excess maleic anhydride, and in most instancesit is preferable to .add the styrene and maleic anhydride in equimolecular proportions.

The slurry orsuspen'sion is heated during the continuous addition thereto of the monomers, hydrocarbon or chlorinated hydrocarbon liquid and catalyst. Thetemperature of the slurry may be varied considerably depending upon the boilingpoint of the hydrocarbon or chlorinated by drooarbon liquid used and th desired molecular weight-of the copolymer. Ingenera'l, it is possible to obtain higher molecular weight-copolymers or polymeric materials by carrying out the con-- tinuous polymerization at low temperatures, for example, temperatures of 40 to 60 0. However, at such low temperatures the reaction rate is usually slowerthan at higher temperatures and iii-such instances the rate of conversion ofmonomers to copolymer is not as fastas may be desired. In such cases the temperature may be increased by proper selection or the hydrocarbon or chlorinated hydrocarbon liquid, and the desired molecular weight can stilibe obtained by proper selection of the hydrocarbon liquid or by the use of suitable chain-transfer agents such as the 'alkyl mercaptans, carbon tetrachloride and the like. In most cases it'i-s not necessary to operate at temperatures in excess of 150 C; High temperature operation, that is, at 150C. or higher is apt to have some disadvantages, for example, the copolymer might tend to gel and agglomerate with the result that subsequent removal of the liquid constituents from the copolymer particles becomes difficult. When temperature below the boiling point of the hydrocarbon or chlorinated hydrocarbon liquid are employed it is usually necessary to carry out the polymerization in an atmosphere of an inert gas such as nitrogen or carbon dioxide.

It is preferable to operate the process at the reflux temperature of the mixture of hydrocarbon or chlorinated hydrocarbon liquidand monomers at atmospheric pressure for several reasons. First, the product tends to be more uniform by virtue of the fact that the temperature of the copolymer slurry is uniform under reflux conditions. Secondly", the temperature of the copolymer slurry is easily controlled'since the heat supplied to the vessel in which the copolymer slurry is heated does not have to be controlled except within rather wide limits, and only need be supplied in an amount suflicient to cause boiling. Thirdly, by carrying out the reaction under re flux conditions, the heat of reaction is taken away by the escaping vapors which are cooled in a condenser and returned to the slurry. This not only provides 'an eflicient way of removing the heat of reaction, but also eliminates the necessity of carrying out the polymerization in anatmosphereof inert gas.

During the-continuous addition of styrene and maleic anhydride monomers,,qhydrocarbon or chlorinated hydrocarbon liquid and polymerization. catalyst ;to the. copolymer slurry- -;in the hydrocarbon or chlorinated. hydrocarbon liquid, a. minor :portion or increment of the copolymer slurry "continuously removed or withdrawn. This. may beaaccomplished in a variety of Ways. Qne very convenient modeofoperation is. to continuouslystirthecopolymer slurryin such a man- HBTSSEtO provide amoreor less uniform distributioniof copolymercparticles throughout the slurry and to allowzthe copolymer slurry to continuonslyoverfiowwthrough a suitable pipe oroutlet hrthe slurrycontainer. Inthis manner the volume of slurry in th container is maintained substantially constant and the amount of slurry withdrawn overx'any particular increment of time is thus "substantially equal to the amount of styrene and :maleic .anhydride, hydrocarbon or chlormated .zhydroc'azcbon liquid and catalyst added to the :copolymer slurry. Another mode of operation consists in continuously withdrawing or removing a minor portion of the slurry at. some point below the surface of the copolymer slurry as by gravity flow or by pumping. Still another way of removing a minor portion of the slurry is to use a container having a conical shaped bottom in which the copolymer particles are permitted to settle and removing the settled copolymer through a suitable pipe or outlet.

The'rate of withdrawal or removal of the slurry from the main portion or body of the copolymer slurry in the hydrocarbon or chlorinated hydrocarbon liquid need not necessarily be the-same as the rate of addition of the styrene and maleic monomers, the hydrocarbon or chlorinated hydrocarbon liquid and the polymerization catalyst over any particular increment of time. However, forease of operation and in order to ob tain the most uniform copolymer, it is preferred to withdraw or remove the slurry at substantially the same rate as the styrene and maleic anhydride monomers, hydrocarbon or chlorinated hydrocarbon liquid and catalyst are added to the main portion or body of the copolymer slurry.

The copolymer slurry obtained in the manner described above, that is, by removal from the main portion or body of the slurry, consists essentially of particles of'styrene-maleic anhydride copolymer, hydrocarbon or chlorinated hydrocarbon liquid, small amounts of polymerization catalyst, and unreacted styrene and maleic anhydride monomers. Usually, the conversion is between about and of the added monomers so that the slurry only contains between about 5' "and 20% by weight of the unreacted monomers. The slurry is run through a suitable filtering device such as a plate and frame filter press, or-through a centrifuge or the like to separate the copolymer particles from the major portion of the liquid constituents of the slurry. At this stage, that is, after filtration or centrifuging the copolymer cake will normally contain between about 35 and 45% by weight of liquid constituents, primarily the hydrocarbon or chlorinated hydrocarbon liquid. These liquid constituents are substantially removed by steaming the copolymer particles or by bringing the copolymer particles into contact with a stream of hot inert gas, or by heating the copolymer particles in-an oven todrive ofi the liquid constituents by evaporation.

The dry or substantially liquid free styrenemaleic anhydride copolymer particles are generally or essentially spherical in shape. The'particles: are substantially. dustless. and dissolve easily inaqueeus alkali solutions. llhey usually have an apparentdensity between about 34 and 40 pounds per cubic foot as compared with an apparent density of 13 to 17 pounds per cubic foot for copolymer particles prepared by batch processes. The styrene-maleic anhydride copolymers of this invention generally hav an average particle size between about 8 and 80 microns. The major portion of the particles have diameters Withinthe range of 40 to 50 microns. A typical screen analysis of the dry copolymer is as follows: on 80' mesh3.2%, on 100 mesh-0.8%, on 200 mesh-37.5%, on 325 mesh-16.1%, and through 325 mesh-42.4%.

The particle size of the copolymer particles is largely-dependent on such factors as the hydrocarbon or chlorinated hydrocarbon liquid used, the temperature at which the process is carried out, the monomer composition and concentration, the type and amountof catalyst used, and the use or non use of modifying agents such as crosslinking agents as, for example, the maleic or fumaric esters of polyhydric alcohols, diisopropenyl benzene, divinyl benzene or the like, and chain-transfer agents, as, for example, alkyl mercaptans such as dodecyl mercaptan, carbon tetrachloride or the like. By proper selection and use of these factors, it is possible to varythe particle size of the copolymer within certain limits. In general, by using slow reaction rates and low concentrations of monomer plus copolymer in the copolymer slurry, it is possible to'obtain large or coarser copolymer particles.

Depending upon the conditions of operation, for example, the hydrocarbon or chlorinated hydrocarbon liquid andtemperatures used, it is also possible to obtain copolymers of low or high molecular weight. The viscosity of a solution of the copolymer is a good way of indicating the molecular Weight of the copolymer. In the absence of cross-linking agents it has been possible to produce copolymers in accordance with this invention which when dissolved to the extent of 5% in a water solution of sodium hydroxide at a pH of 8 and a temperature of 25 C. have a viscosity of 5 to 85 centipoises. When crosslinking agents are employed, however, the viscosity may be much higher, up to or just below the point where the polymer becomes insoluble.

The terms non-polymerizable, inert hydrocarbon liquid or hydrocarbon liquid as used herein are intended to cover the aromatic hydrocarbons as, for example, benzene, toluene, xylene and the like; alkanes such as heptane, hexane, octane, nonane and the like; mixtures of aromatic hydrocarbons with alkanes; cyclo alkanes such as cyclohexane and cyclopentane and the like. The

terms non-polymerizable, inert chlorinated hy-.

drocarbon liquid or chlorinated hydrocarbon liquid as used herein are intended to cover the chlorinated aromatic hydrocarbons as, for example, chlorobenzene, dichlorobenzene, chlorotoluene and the like; mixtures of such chlorinated hydrocarbons with alkanes; and chlorinated alkanes such as ethylene dichloride, carbon tetrachloride and the like. Benzene enables th preparation of higher molecular weight copolymers than is possible with the use of toluene or xylene. Mixtures of benzene and the alkanes are particularly suitable for producing lower molecular weight copolymers. When using the higher boiling aromatic hydrocarbon-liquids such as toluene or xyleneit is o'itendesirable to use such liquids together with the low boiling alkanes such as he ptane or hexane when lower molecular weight copolymers are desired, particularly when the process is operated at reflux temperatures. It is preferable to employ aromatic hydrocarbons con taining from 6 to 9 carbon atoms, and not more than 2 chlorine atoms, alkanes containing from 5 to 10 carbon atoms or chlorinated alkanes containing from 2 to 5 carbon atoms and not more than 4 chlorine atoms.

Generally, the alkanes do not dissolve substantial quantities of maleic anhydride and when such monomer is employed it is preferred to use other hydrocarbon or chlorinated hydrocarbon liquids or mixtures of alkanes and other hydrocarbon liquids such as the aromatic hydrocarbons.

It is possible to use vinyl compounds other than styrene in the processes hereinbefore described. For example, it is possible to replace the styrene completely or partially with liquid vinyl compounds such as vinyl acetate, vinyl ethers, divinyl benzene, p-chloro styrene, p-methyl styrene and the like. It is also possible to use gaseous vinyl compounds having a single vinyl group and which are readily soluble in the hydrocarbon or chlorinated hydrocarbon liquid as, for example, vinyl chloride, providing the process is carried out under pressure in a suitable pressure resistant vessel. The maleic anhydride may be replaced completely or partially by hydrocarbon soluble ethylene 0a,,6' dicarboxylic anhydrides such as itaconic anhydride or citraconic anhydride, or by unsaturated alkylene mono-carboxylic acids such as acrylic acid or methacrylic acid, or the maleic anhydride may be replaced to the extent of 50% by weight by alkyl esters of maleic acid containing from 1 to 10 carbon atoms in the alkyl group,

particularly the alkyl half esters of maleic acid.

Particularly valuable terpolymers are prepared by using a mixture of styrene, maleic anhydride and acrylic acid and/or methacrylic acid. Particularly suitable proportions of these monomers consist of 40 to 65% by weight of methacrylic acid or acrylic acid, 15 to 40% by weight of styrene and 10 to 30% of maleic anhydride.

Terpolymers have also been prepared successfully from a mixture of vinyl acetate, maleic anhydride and acrylonitrile, or a mixture of styrene, maleic anhydride and acrylonitrile.

It is also possible according to the processes of this invention to prepare homopolymers of acrylic acid, methacrylic acid, acrylamide, acrylonitrile and other polymerizable unsaturated compounds containing polar groups as, for example, carboxyl, carboxylic anhydride, amide and nitrile groups. Such monomers are normally soluble in one of the inert hydrocarbon or chlorinated hydrocarbon liquids and the homopolymers prepared therefrom are normally insoluble and non-swell-;

able in such hydrocarbon or chlorinated hydrocarbon liquids.

It is to be understood that the invention is not limited to the continuous polymerization of the specific unsaturated compounds named herein or.

to the use of a non-polymerizable, inert hydrocarbon or chlorinated hydrocarbon liquid, since it is possible to obtain similar results by usingother polymerizable unsaturated organic compounds in such inert hydrocarbon or chlorinated hydrocarbon liquids or in other non-polymerizable inert liquids which are solvents for the monomer or monomers but are non-solvents and nonswelling media for polymeric materials derived from such unsaturated compounds.

In general, it is possible to prepare homopolymers, copolymers and heteropolymers having substantially the same particle size characteristics,

freedom from dusting, and apparent density as a cmsvo.

9 the copolymers prepared from styrene and Imaleic anhydride, byproper selectionofr anon-polymerizable, inert liquid, temperature, type and amount of catalyst etc.

A large .varietyof polymerization catalysts may be used in thezproce'sses of. this invention dependingron thermonomer or monomers used 1 and other factors; Astexamples' of catalysts which are generally suitableimay be mentioned the dialkyl disulfides suchas diamyl disulfide, ditertiary dodecyl. disulfide and the like; azo compounds suchuasmd azoxbis isobutyronitrile and.

the like; perbenzoatessuch. as ditertiary butyl perbenzoate; dialkyl peroxides such. as rditertiary butyl peroxide, ditertiary amyi peroxidediethyl peroxideand thellike; and: some acyllperoxides such. as. lauroyl peroxide, benzoyl peroxide and the like; and; hydroperoxides suchiasr tertiary butyl hydroperoxide and cumene hydrop'eroxide.

One of the importanttiadvantagesof the continuous polymerization processes of this invena ti-omin additionto those hereinbeiore disclosed, is:that theseprocesses'may facilitate in some casesgproduction oficopolymers in a large variety of ratios of the'various comonomers. Thus, it is possible to add continuously monomers of the desired polymer composition, but the actual monomeriratios inthe' polymer slurry-could be difierent from thisyaas needed, to form the desired polymer: Thefiltrate and washings from separe-ted polymer slurry -would contain the unreactedmonomers of this diirerent composition necessary ror production' or the desired polymer.

A further understanding of the present invention will beobtained from the following specific examples whieh are' intended to illustrate the invention but notto limit the scope thereof, parts and percentagesbeing by weight.

Ezwmple I" A:- solution in benzene of styrene plus m'aleic: anhydride monomers in equimolar proportions and containing additionally 0.05% benzoyl pero'xide was heated'at the refluxing temperature-(82 (7.) in a vessel'equipped with an overflowtube, a stirrer'andaireflux condenser. The mixture 'was stirred vigorously andheated-at reflux-temperature until 90% of the monomers were converted to styrene-'maleic copolymer, which required about li hours. The styrenemaleicc'anhydride "copolymer separated from the benzene. in theaform of extremely-fine: particles and were .maintainedrin a suspended state by thewvigorous agitation. This wasthe initial copolymer slurryi A 32% solution in benzenexof styrene plus maleic anhydride: monomers in. equimolar proportions and containingiadditionally 0.05% benzoyl peroxide was added continuously to the initial copolymer slurry at the rate of 10% per hour, ,basedfon theweight of the initial copolymerslurry in. the reaction .vessel. The copolymer slurry. wasstirredyigorously and sufficient heat was continuouslysupplied to maintain gentle refluxingor the benzene. in the slurry. Copolymer slurrywascontinuouslylremoved from the vessel through the overflow pipe at substantially the same zrate thatthe monomer solution was added. Thewcopolymer in the overflow slurrywas separated iromtheliquid constituents therein by filtration. Thev filter cake: was washed with benzenesandtlren dried'in an ovenat 105 C. to complete-the removalof liquid.- The filtrate and washings. were; analyzed and used as a portion 0143116 charge tctbereaction vessel.

Conversion of monomers tocopolymer over a period of several days averaged 90 to' 95% and Copolymer recovery was in excess of 96% of reacted monomers. The dry product was afreeflowing, substantially dustless powder, easily soluble in aqueous solutions ofalkali. A 5% solution of the product in a water solution of sodium hydroxide at a pH of 8.0 had a viscosity of centipoises at 25 C. The dry copolym'er had an.

apparent density of 35 pounds per cubic foot.

Example II t A continuous polymerization process wascarried out in substantially the same manner as described in Example I, except that a 25% solution in benzene of styrene plus maleic anhydride monomers in equimol-ar proportions and containing additionally 0.035% benzoyl peroxide was continuously added to the initialcopolymer slurry at the rate of 8% per hour,1based on the weight of the initial copolymer slurry in the reaction vessel. Copolymer slurry was continuously removed at substantially the same rate through an overflow pipe.

A 5%solution of the copolymer' product-inn water solution of sodium hydroxide'at apH of 8.0 had a viscosity of centipoises zit- 25 G;

The dry copolymer product had an apparent density of '36 pounds per cubic foot.

Example III A continuous polymerization process was carried out in substantiallythe same manneras de scribed in Example 1, except that a 30% solution of benzene of styreneplus maleic anhydride monomers in equimolar proportions and contaim ingadditionally 0.06% of benaoyl peroxide wa's added continuously to the initial co'p'olymer slurry at :the rate of 12% per hour, based on the weight of the initial .copolymerslurry'inthe reaction vessel. Copolymer slurry was continuously removed at substantially the same rate through an overflow pipe.

A 5% solution of the copolymer product in-a The mixture was stirred vigorously andheated at reflux temperature until 88% of the. monomers were converted toa styrenc-maleic anhydridemethyl acid maleate terpolymer, which required about 3 hours. The terpolymer separated from the benzene-n-heptane solution in the formof extremely fine particles which weremaintained in a suspended state by the vigorous agitation of the slurry. This was the initial tor-polymer slurry. A solution containing 15.3% styrene, 11% maleic anhydride, 3.6%.methyl acid maleate, 0.1% benzoyl peroxide, 50% benzene and 20% commercial n-heptane was continuously. added to the initial terpolymer' slurry, as prepared above, at the rate of 8% of the solutionpei hour,

based on the weight of the initial terpolymer slurry in the reaction. vessel. The terpolymer slurry was stirred vigorously'and suflicient heat was continuously supplied to maintain gentle refluxing of the benzene-n-heptanemixture in the slurry. Terpoiymerslnrrywas continuously 11 removed from the vessel through the overflow pipe at substantially the same rate that the monomer solution was added. A dry terpolymer was recovered from the overflow slurry using the procedure described in Example I.

Conversion of the monomers to terpolymer over a period of '72 hours averaged about 88%. The productgdensity was similar to that of the product prepared as described in Example I, but a solution of the terpolymer in a water solution of sodium hydroxide at a pH of 8.0 had a viscosity of centipoises at C.

A continuous polymerization process was carried out in substantially the same manner as described immediately above except that benzene was used as the hydrocarbon liquid instead of a mixture of benzene and n-heptane. A 5% solution of the resulting terpolymer in a water solution of sodium hydroxide at a pH of 8.0 had a viscosity of 40 centipoises at 25 C.

Example V A substantially dry terpolymer containing about 50.3% styrene, 48.7% maleic anhydride and 1% divinyl benzene in chemically combined form was first prepared by heating the equivalent monomers in xylene using benzoyl peroxide as a catalyst and then separating the terpolymer from the liquid constituents. The terpolymer was in the form of extremely fine particles and was added to an amount of xylene sufiicient to provide a 15% terpolymer slurry. This was the initial terpolymer slurry.

A solution containing 12.4% styrene, 12.0% maleic anhydride, 0.6% of 40% divinyl benzene (containing also vinyl ethyl benzene and diethyl benzene), 0.05% benzoyl peroxide and 74.95% xylene was continuously added to the initial terpolymer slurry at the rate of 8% per hour, based on the weight of the initial terpolymer slurry in the reaction vessel. The terpolymer slurry was stirred vigorously and the temperature of the slurry was maintained as close to 80 C. as possible. Terpolymer slurry was continuously removed from the vessel through an overflow pipe at substantially the same rate that the. monomer solution was added. The overflow terpolymer slurry was filtered, and the filter cake washed with xylene and heated in an oven at 150 C. to

drive oif the liquid. The polymer filter cake,

after filtration, contained about 62% of the terpolymer. A filter cake of the same terpolymer prepared by the batch process will normally only contain about 24% of the terpolymer. The conversion of monomers to the terpolymer over a period of 72 hours averaged about 88%.

The dry terpolymer was a free-flowing, substantially dustless product having an apparent density of 38 pounds per cubic foot. A product prepared by the batch process was extremely light, fluffy and dusting and had an apparent density of 14 pounds per cubic foot.

A continuous polymerization process. was carried out in substantially the same manner as immediately described above, except that benzene was used as the hydrocarbon liquid instead or xylene and 0.1% to 0.2% of 40% divinyl benzene instead of 0.6%. A substantially similar product was obtained. 7

Example VI A solution containing 3% acrylic acid, .8% styrene, 1.2% maleic anhydride, .05% benzoyl peroxide and 94.95% benzene washeated at refluxing temperature (82 C.) in a vessel equipped with a stirrer and a'reflux condenser until a polymer haze developed after which, a solution containing 14% acrylic acid, 8.4% styrene, 5.6% maleic anhydride, 0.25% benzoyl peroxide and:

the remainder, benzene, was added continuously to the initial terpolymer slurry at the rate of 7.6% per hour, based on the weight of the initial copolymer slurry in the reaction vessel. The

terpolymer was stirred vigorously and sufficient heat was continuously supplied to maintainv gentle refluxing of the benzene in the slurry; Terpolymer slurry was continuously removed from the vessel through an overflow pipe at substantially the same rate that the monomer solution was added. The terpolymer in the over-:

flow slurry was separated from the liquid constituents of the slurry by filtration, washing the filter cake with benzene and then drying in a current of hot air at a temperature of C.

The filtrate contained the monomers in the weight ratio of 60 parts of acrylic acid to 16 parts of styrene to 24 parts of maleic anhydride.

Conversion of monomers to terpolymer over a period of '72 hours averaged 88%. The apparent density of the dry terpolymer product, which was free-flowing and substantially dustless, was 28 pounds per cubic foot.

A continuous polymerization process was car-- ried out substantially in the same manner as described immediately above except that meth-- acrylic acid was used instead of acrylic acid, and th methacrylic acid, styrene and maleic anhy-1 dride were employed in a weight ratio of 65 :20:15.,

The product was similar to that obtained with acrylic acid.

Water s lutions r the p rtial alkali metal or. ammonium salts of the above described terpoly--- mers of styrene, maleic anhydride and acrylic;

acid or methacrylic acid are especially suitable. for sizing nylon warp yarns preparatory to weaving.

The products produced in accordance with the wide variety of uses.

coatings.

for use in the textile industry.

Various changes and modifications may .be' made in the operation of the processes described 5 herein. Thus, if more complete conversion of the monomers is desired a number of reactors may be used in series and fresh catalyst or-modifier may be added to the reactors following the initial reactor in order to alter the rate of reac i tion or the polymer properties. What is claimed is:

1. A continuous process of polymerizing monomers of polymerizable unsaturated organic compounds which comprises continuously adding a. polymerization catalyst, a non-polymerizable inert liquid, styrene and an unsaturated compound selected from the group consisting of maleic anhydride, mixtures of maleic anhydride and alkylesters of maleic acid, said mixtures containing a at least 50% of maleic anhydride by weight, mixtures of maleic anhydride and acrylic acid and mixtures of maleic anhydride and methacrylic acid, to a slurry of a polymer of styrene and saidunsaturated compound in said inert liquid, said inert liquid being anon-solvent and'non-swelh chlorinated hydrocarbons, continuously maintaining the temperature of said slurry sufiiciently high to effect polymerization of the monomers of styrene and said unsaturated compound in the slurry thereby forming additional polymer of styrene and said unsaturated compound, and continuously removing a minor portion or the slurry from the built of the sulrry.

2. A continuous process substantially according to claim 1 but further characterized in that the polymer the minor proportion of slurry is separated from the major portion of the liquid constituents in the slurry and then subjected to heat to remove a substantial portion or the liquid contained therein.

3. A continuous process of polymerizing sty- Irene and maleic anhydride which comprises continuously adding styrene, maleic anhydride, a polymerization catalyst, and a non-polymerizable inert liquid, to a slurry of a copolymer of styrene and maleic anhydride in said inertliquid, said inert liquid being a non-solvent and nonswelling medium for said copolymer and being selected from the group consisting of hydrocarbons and chlorinated hydrocarbons, continuously maintaining the temperature of said slurry sufficiently high to effect polymerization of the monomers of styrene and maleic anhydride in said slurry thereby forming additional copolymer of styrene and maleic anhydride, and continuously removing a portion of the slurry from the bulk of the slurry at such a rate that the volume of the bulk of the slurry remains substantially constant.

4. A process of continuously polymerizing styrene and maleic anhydride which comprises continuously adding a polymerization catalyst, a non-polymerizable, inert liquid and substantially equimolar proportions of styren and maleic anhydride monomers in a weight ratio of 0.02 to 0.3 parts of catalyst to 80 to 60 parts of said liquid to to 40 parts of said monomers, to a slurry of a copolymer of styrene and maleic anhydride in said inert liquid, which slurry contains additionally unreacted styrene and maleic anhydride monomers and a polymerization catalyst, said continuous addition of catalyst, inert liquid and styrene and maleic anhydride monomers being mad at the rate of 8 to 12 by weight per hour, based on the weight of the initial slurry, said inert liquid being a non-solvent and nonsvvelling medium for said copolymer and being selected from the group consisting of hydrocarbons and chlorinated hydrocarbons, continuously maintaining the temperature of said slurry sufficiently high to effect polymerization between the styrene and maleic anhydride monomers in said slurry thereby forming additional quantities of a copolymer of styrene and maleic anhydride, and continuously removing a portion of the slurry from the bulk of the slurry at a rate such that the volume of the bull: or the slurry is maintain d substantially constant.

5. A process substantially according to claim 4, but further characterized in that the inert liquid is benzene.

6. A process substantially according to claim 4, but further characterized in that the temperature of the slurry is continuously maintained at the reflux temperature of the inert liquid in the slurry.

'7. A continuous process of polymerizing styrene, maleic anhydride and acrylic acid which comprises continuously adding a polymerization catalyst, a non-polymerizable, inert liquid, sty- 1.4? rcne, maleic anhydride and acrylic acid, to a slurry of a terpolymer of styrene, maleic anhy-- dri-de and acrylic acid in said inert liquid, said inert liquid being a non-solvent and non-swelling medium for said terpolymer and being selected from the group consisted of hydrocarbons and chlorinated hydrocarbons, continuously maintaining the temperature of said slurry sufiiciently high to effect polymerization of the styrene, maleic anhydride and acrylic acid monomers in said slurry thereby forming additional terpolymers of styrene, maleic anhydride and acrylic acid, and continuously removing a portionof the slurry from the bulk of the slurry at such a rate that the volume of the bulk of the slurry remains substantially constant.

3. A continuous process of polymerizing sty-- rene, maleic anhydride and methacrylic acid which comprises continuously adding a. polymerization catalyst, a non-pelymerizable, inert liquid, styrene, maleic anhydride and methacrylic acid, to aislurry of a terpolymer of styrene, maleic anhydride and methacrylic acid in said inert liquid, said inert liquid being a non-solvent and non-swelling medium for said terpolymer and being selected from the group consisting of hydrocarbons and chlorinated hydrocarbons, continuously maintaining the temperature of said slurry sufficiently high to effect polymerization of the styrene, maleic anhydride and methacrylic acid monomers in said slurry thereby forming additional quantities of a terpolymer of styrene, maleic anhydride and methacrylic acid, and continuously removing a portion of the slurry from the bulk of the slurry at such a rate that the volume of the bulk of the slurry remains substantially constant.

9. A composition of matter consisting essentially of free-flowing, substantially dustless particles of a copolymer of styrene and maleic anhydride, said particles being essentially spherical and having an average particle diameter between 8 and 80 microns and an apparent density between about 34 and 40 pounds per cubic foot.

10. A continuous process of polymerizing monomer of polymerizable unsaturated organic compounds which comprises continuously adding a polymerization catalyst, a non-polymerizable inert liquid, a liquid vinyl compound and an unsaturated compound selected from the group consisting of maleic anhydride, mixtures of maleic anhydride and alkyl esters of maleic acid, said mixtures containing at least 50% of maleic anhydride by weight, mixtures of maleic anhydride and acrylic acid and mixtures of maleic anhydride and methacrylic acid to a slurry of a polymer of said liquid vinyl compound and said unsaturated compound in said inert liquid, said inert liquid being a non-solvent and nonswelling medium for said polymer and being selected from the group consisting of hydrocarbons and chlorinated hydrocarbons, continuously maintaining the temperature of said slurry sufiiciently high to effect polymerization of the monoof maleic anhydride and alkyl esters of maleic acid, said mixtures containing at least 50% of maleic anhydride by weight, mixtures of maleic anhydride and. acrylic acid and mixtures of maleic anhydride and methacrylic acid, said particles being essentially spherical and having an average particle diameter between 8 and 80 microns and an apparent density between 28 and 40 pounds per cubic foot.

2. A continuous process of polymerizing vinyl acetate and maleic anhydride which comprises continuously adding vinyl acetate, maleic anhydride, a polymerization catalyst and a non-polymerizable, inert chlorinated hydrocarbon liquid, to a slurry of a copolymer of vinyl acetate and maleic anhydride in said inert liquid, said inert liquid being a non-solvent and non-swelling medium for said copolymer, continuously maintaining the temperautre of said slurry sumciently high to eiiect polymerization of the monomers of vinyl acetate and maleic anhydride in said slurry, thereby forming additional copolymer of References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,375,256 Soday May 8, 1945 2,378,138 Gaylor Jun 12, 1945- 2,383,399 Lundquist Aug. 21, 1945 2,392,585 Fryling Jan. 8, 1946 2,396,785 Hanford Mar. 19, 1946 2,522,775 Bryant Sept. 19, 1950' OTHER REFERENCES Burleson, Vinyl paste resin, Modern Plastics, 24, 108-111, August 1947. 

1. A CONTINUOUS PROCESS OF POLYMERIZING MONOMERS OF POLYMERIZABLE UNSATURATED ORGANIC COMPOUNDS WHICH COMPRISES CONTINUOUSLY ADDING A POLYMERIZATION CATALYST, NON-POLYMERIZABLE INERT LIQUID, STYRENE AND AN UNSATURATED COMPOUND SELECTED FROM THE GROUP CONSISTING OF MALEIC ANHYDRIDE, MIXTURES OF MALEIC ANHYDRIDE AND ALKYL ESTERS OF MALEIC ACID, SAID MIXTURES CONTAINING AT LEAST 50% OF MALEIC ANHYDRIDE BY WEIGHT, MIXTURES OF MALEIC ANHYDRIDE AND ACRYLIC ACID AND MIXTURES OF MALEIC ANHYDRIDE AND METHACRYLIC ACID, TO A SLURRY OF A POLYMER OF STYRENE AND SAID UNSATURATED COMPOUND IN SAID INERT LIQUID, SAID INERT LIQUID BEING A NON-SOLVENT AND NON-SWELLING MEDIUM FOR SAID POLYMER AND BEING SELECTED FROM THE GROUP CONSISTING OF HYDROCARBONS AND CHLORINATED HYDROCARBONS, CONTINUOUSLY MAINTAINING THE TEMPERATURE OF SAID SLURRY SUFFICIENTLY HIGH TO EFFECT POLYMERIZATION OF THE MONOMERS OF STYRENE AND SAID UNSATURATED COMPOUND IN THE SLURRY THEREBY FORMING ADDITIONAL POLYMER OF STYRENE AND SAID UNSATURATED COMPOUND, AND CONTINUOUSLY REMOVING A MINOR PORTION OF THE SLURRY FROM THE BULK OF THE SLURRY. 